This invention relates to cathode starting sheet assembly machines. The term starting sheet is applied to the relatively thin sheet which initially comprises the cathode in copper, nickel and other refining. The sheets are made of pure copper or nickel 8 typically are about 1,000.times. 1,000.times. 8mm thick and are required in large numbers for both electro-winning and electro-refining plants. With typical cathode weights of 140-160 kgs (as in refining/electro-winning plants) some 1,200-2,800 sheets are required per day for a cathode production of 50,000 tons per year. The starting sheets in copper refining are suspended in the tanks by horizontal bars which pass through one or more inverted U-shaped loops, the lower ends of the limbs of the loops being rivetted to the upper edge of the starting sheet. In the case of nickel sheets the loops are spot welded rather than rivetted. It is a well known fact that the sheet is susceptible to distortion during handling. Unless it is flat and hanging vertically when placed in the electrolitic cell the efficiency of the process is seriously reduced. A considerable proportion of the labour employed in the tank-house is involved in the stripping and assembly of the starting sheets. If their quality is poor and particularly if they are bent or warp in service, and do not hang vertically, the current efficiency and cathode output of the tankhouse can be seriously diminished.
In the earliest refineries of any size the loops were attached to the sheets by means of conventional mechanical presses fitted with special tools. Two men were required at each machine and they passed the assembled sheets onto other men who pounded the sheet flat, pushed the suspension bar through the loops and manually placed the assembled sheet in a storage bolster. Generally when flattening the sheets the men beat in them a shallow diagonal cross which tends to stiffen the sheet. Because the quality of the sheets was often poor it was usual in those days to remove each two day old cathode from the cells for a short while in order to beat it flat again on an inclined stand which was mobile and used on the top of the cell. This operation was called "wet flapping".
In the late 1960's because of increasing labour costs and the difficulty in some countries of obtaining labour at all willing to perform the above mentioned type of work, new methods of preparing the sheets were developed. The most successful was an automatic sheet assembly machine developed at Boliden, Sweden, in 1960 which was later marketed by C. J. Wennberg A.B. This progressive automation is described in the transactions of the metallurgical Society of A.I.M.E. Volume 236 pages 1570-1573, published November 1966. This described an automated system installed in a new tankhouse at the copper refinery at Boliden, Sweden. In that process flattened sheets are fed horizontally along a processing path and the loops and bars are connected to the sheets whilst they are in their horizontal position, whereafter the sheets are turned through 90.degree. whilst still in their horizontal plane, and then turned vertically and placed on a storage conveyor. A machine of this type is also shown in British Specification No. 957,962 and its corresponding U.S. Pat. No. 3,199,170.
Another British Specification No. 115,713 in the name of Wennberg also shows a similar apparatus wherein the starting sheets are again turned from a horizontal position to a vertical position. During such turning there is a danger of distortion of the sheet unless it is fully supported throughout the transfer period.
Besides the machines referred to above, others having a roughly similar capacity and degree of automation are known to those engaged in the art but in all of them the sheet is moved, rivetted and assembled in a substantially horizontal position until it is finally transferred to a vertical position on the storage or spacing conveyor or rack. This is true even of the very latest models of the aforementioned machines.
As has been mentioned, the processes and apparatus which have been referred to in these prior documents are in general automatic processes which have led to the minimisation of the amount of labour involved and whilst this objective is a very desirable one, particularly where labour costs are high, it does involve the design of relatively complicated machinery which can for example for a complete starting sheet assembly machine of high capacity (say 600 sheets per hour) cost in the order of 300,000, ($600,000).
Apart from the high cost involved, a common weakness of high automation is that the slightest breakdown in one of the many parts of the machine causes the whole of the machine to have to be stopped until the fault is rectified. During all this time the three of four operators or supervisors attending the machine are idle and its entire output is lost. These machines also occupy considerable floor space since the sheets are moved through the machine in a horizontal position and only after assembly is completed are they upended to a vertical position for placing on the storage conveyor. As has been mentioned, while being upended the sheet has to be fully supported since otherwise it would be bent or damaged. The stop - go movement of the sheets through the preceding sections of the machine at high speed is also troublesome because, to minimise inertia the conveyor mechanisms are made as light as possible and accurate sheet location and guidance is difficult to maintain. Without exception, all the high automated high speed machines previously referred to, handle the sheets horizontally until placing them on the storage conveyor.
The present invention is of particular application in areas where labour availability is considerable and local labour costs relatively low and the invention starts from the premise that in such circumstances it is better to use say two or more slower and simpler machines which are together capable of the same total output as a fully automatic high speed one. Even though the attendant labour may be increased by one or two the capital cost is considerably less and the reliability greater. The lost labour time and lost sheet production is also reduced since it is unlikely that both machines would be simultaneously out of order. The time and money spent on maintaining the one large high speed fully automated machine in servicable condition is always quite considerable, and likely to be at least equal, if not more, than that of maintaining two machines of the same total capacity, since their slower individual speeds permits the use of simpler constructions and handling mechanisms.